Electrostatic writing system utilizing tapped delay lines



y' 20, E. D. JONES ETAL 3,196,451

ELECTROSTATIC WRITING SYSTEM UTILIZING TAPPED DELAY LINES Filed May 16, 1962 SOURCE OF F l G. I. FACSIMILE VIDEO SIGNALS /l0 l3 SOURCE OF SOURCE OF NEGATIVE POSITIVE PULSES PULSES freq. fl freq. f2

MODULATOR CIRCUIT W 42\D 44F kg F G. 2.

34 38c 4oc- 42a 44 8 4ea- -4eo :senzs 4oa- /4ac.

2 3 38A 488 l 1 'l 0 SOURCE 9 42A 44A 46A 48A 5s NEGATHE 6 PULSES 52 54 s freq. f1 j v v SOURCE OF SOURCE OF T- POSITIVE VIDEO PULSES SIGNALS as "yo fveq. f2

VOLTAGE SOURCE OF 1 CONTROLLED POSITIVE I EARl-E D- NE TIME P s 1- ALBERT MACOVSKI DELAY freq. f2 INVENTORS.

OF 72 BY afou/ffi A v S|GNALS "75 s ATTO RN EYS.

United States Patent 3,196,451 ELECTRUSTATIC WRITING SYSTEM UTILIZING TAPPED DELAY LINES Earle D. tones, Menlo Park, and Albert Macovski, Palo Alto, Calif., assignors to Standard Research Institute,

Paio Alto, Calif., a corporation of California Filed May 16, 1962, Ser. No. 195,250 4 Claims. (Cl. 346-74) This invention relates to electrostatic-writing systems, and more particularly, to improvements therein.

An electrostatiowriting system usually involves some apparatus for depositing electrical charges on paper in a pattern having an arrangement in accordance with the intelligence desired to be written. Thereafter, a toner powder is dusted onto the paper. The powder adheres only to those areas of the paper wherein there is an electrostatic charge. Thereafter, heat may be applied to permanently fix the powder to the paper. Thus, the intelligence, which was initially conveyed to the paper in the form of a charge pattern, now appears as a visible pattern.

Various arrangements have been provided for depositing electrostatic charges on paper in accordance with information received from signals. One system is to provide a delay line from which many taps are taken from diiierent points along the delay line. These taps are terminated as writing styli above an insulating surface, upon which it is desired to deposit an electrostatic charge. A bar of conductive metal is located on the side of the paper opposite to which the writing styli are brought and, further, is located opposite to the paper. Thus, the paper is moved between the writing styli and the back bar. A pulse is applied to one end of the delay line. The amplitude of the pulse is such that in and of itself it will not cause an electrical discharge from ony one of the styli. However, a signal can be applied to the back bar, having an amplitude such that, when it is pulsed simultaneously with a pulse on any one of the styli, an electrical discharge will take place. By synchronizing the application of a pulse to the delay line, with the time of the application of a signal to the back bar and the motion of the paper, the charge pattern can be laid down on the paper in a manner to convey intelligent information.

One of the problems which arises with a system of this type occurs when it is desired to increase the number of writing styli, so that the writing density is increased. If the number of styli are increased, it is necessary to increase the number of taps made to the delay line.

However, then it is necessary to insure that a pulse exists on only one tap at any instant, which requires a line which has a delay-to-rise-time ratio equal to the number of taps. At present, the maximum number of taps available j on lines having delay-to-rise ratios equal or greater than the number of taps is on the order of 100, and these are expensive. Lines having 30 to 40 taps are readily available at 'a reasonable cost.

An object of this invention is the provision of an electrostatic-writing system of the type employing a tapped delay line, whereby the number of writing styli employed may be increased without an inordinate increase in the system.

Yet another object of the present invention is the provision of a novel and unique electrostatic-writing system of the type employing tapped delay lines.

3,196,451 Patented July 20, 1965 In a system of delay-line scanning using a tapped delay line, writing must occur only in the presence of both the scan pulse and a back-bar pulse, and not due to each pulse alone. This requires the achievement of two important characteristics: first, a sharp threshold mechanism, and, second, the ability to write in extremely short time durations. Existing electrosensitive papers fill neither of these requirements.

A further object of the present invention is the provision of a writing technique which affords a sharp threshold mechanism and the ability to write in extremely short time durations.

These and other objects of the invention may be achieved in an arrangement wherein, for the purpose of achieving the required sharp threshold mechanism and the ability to Write in extremely short time durations, advantage is taken of the fact that, when a stylus is given a point, it has emission properties such that a threshold must be exceeded in order that a discharge take place. Such threshold is dependent upon the radius of curvature of the point of the stylus. The threshold action is very sharp, and the field-emission phenomenon is very rapid, occurring in small fractions of a microsecond.

The problem of increasing the number of writing styli is solved by arranging the styli in groups distributed across the paper and connecting one stylus in each group to a different delay-line tap. The back bar consists of a plurality of back bars, each one of which covers the region underneath a group of styli. The plurality of back bars are connected to taps on a delay line, which provides a delay suflicient to insure that a back bar will be pulsed during the interval required to scan the group of styli.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood FIGURE 2.

frequency f1, and a source of positive signals 12 at a fre-' quency f2. The frequencies are selected so that the linescanning rate of the facsimile system is equal to the difference fl-f2. The facsimile signals are derived from a source 14.

The source of negative pulses is connected through a resistor 16 to one end of a delay line 18. The other end of the delay line is connected through an impedafiematching resistor 20 to ground. The delay line has a. plurality of taps, each of which is connected to a different stylus 22A through 22G. Each one of the styli 22A through 22G has the end thereof extended, to contact or to be in close proximity to paper 24, from which it is desired to deposit an electrostatic charge. A conductive backplate 26 is positioned on the side of the paper oppositeto the side contacted by the ends of the styli and etfectively extends to cover the region of the paper which is covered by the styli.

The styli can be imbedded in an insulator, such as glass, with the ends flush against the surface, to avoid tearing the paper. The source of facsimile video signals and the source of positive pulses are both connected to a modulator circuit 28, which serves the function of modulating the pulse amplitude with the video signals. The output of the modulator circuit is applied to the back bar 26. It is only in the presence of a signal from the video signal source 14 thatthe positive pulses are applied to the back bar such that a deposit of charge can occur.

In an embodiment of the invention which was built, it was found that, by way of example, 600 volts existing between stylus and back 'bar would not cause writing, while 800 volts would cause deposition of a developable .charge image of high contrast. Thus, in the arrangement shown in FIGURE 1, the negative-pulse source may continually apply pulses to the electrostatic writing transducer comprised by the tapped delay line, the styli connected thereto, and the :back bar. No writing will result, however, until a video signal is received from the source of facsimile video signals, Thus, if the paper 24 is moved in sy-nchronism with the original copy being scanned at the facsimile transmitter, the arrangement shown in FIG- URE 1 can reproduce the original copy.

FIGURE 2 is a circuit arrangement which illustrates how the problem of achieving a plurality of styli, using an inexpensive tapped delay line, may be solved. A source of negative pulses 30, .at a frequency fl is connected through an impedance-matching resistor 32 to a mult-itap delay line 34. The other end of the delay line is connected to ground through an impedance-matching resistor 36. QE-ach one of the taps of the delay line 34 is connected to a bus bar, respectively 38A, 38B, 38C, and 39D. The bus bar 38A is connected to one stylus 40A, 4 2A, 44A, 445A, 48A, in each group of styli. The bus bar 3833 is connected to a second stylus, respectively 40B, 42B, 44B, 46B, and 488 in each group of styli. The bus bar 380 is connected to a stylus, respectively 40C, 42C, 44C, 46C, and 48C in each group of styli. The bus bar 38D is connected to a different stylus, respectively 40D, 42D, 44D, 46D, and 48D in each group of styli. The styli all contact one side of the paper 49.

On the other side of the paper 49 there is positioned a backplate, respectively 50, 52, 54, 56, and 58 for each group of styli. These associated baclcplates are positioned on the opposite side of the paper 49, in order to oppose each group of styli and cover the area thereunder.

The backplate is connected to a second multiple-tap delay line 60. A source of positive pulses 62 is connected to one end of the delay line 60, through a resistor 64, and to the other end of the delay line 60, through a second impedance-matching resistor 66. A source of video signals 6-8 is connected to ground and to one side of the source of positive pulses 62 at the junction 70, in a manner so that, in the presence of a video signal, the entire delay line 60 is raised in potential substantially by the amplitude of the potential applied from the source of video signals.

The repetition frequency of the source of negative pulses should be the product of the frequency of positive pulses times the number of back-bar segments. The reason for this is that it is desired that each group of writing styli have a pulse applied thereto while a pulse is applied to a back-barsegment, Thus, for example, a negative pulse is applied to the delay line 34. As this pulse travel-s down the delay line, it will be applied to one stylus in each group of styli. However, if the back bar 50 has a positive pulse applied thereto at that time, then writing will occur only under styli 40A, 40B, 49C, and 40D, and not under any of the other styli, provided, however, that in addition a signal is present from the source of video signals 63. In order to achieve writing under the second group of styli, respectively 42A, 423,

a a 42 C, and 42D, it is necessary to apply a pulse from the negative-pulse source 30 again to the delay line 3-4. Meanwhile, the pulse from the source of negative pulses 612 has traveled down to the second back-bar segment 52.

In this manner, by making the source of positive pulses have a frequency equal to that of the line-scanning rate of a facsimile system, and, by making the source of negative pulses equal to five times the line-scanning rate, and, by moving the paper $9 at a rate equal to the rate at which each line element on the original facsimile is being scanned, a charge deposition is laid down which can be developed into an intelligible picture.

It should also be obvious that the styli and back-bar arrangements shown in FIGURE 1 and/ or FIGURE 2 may also be employed for writing video signals of any type, whether of the facsimile type or otherwise, provided the frequencies of the scanning pulses are maintained in synchronism with the frequencies employed at the source of video signals.

For example, an oscillographic recording system can be constructed using the structure shown in FIGURE 2. In oscillographic recording, the deflection of the writing spot should be proportional to the amplitude of the analog signal. This can be accomplished by substituting, for the source of video signals 68, the circuits represented by the block diagram of FIGURE 3. Here, positive pulses at the rate 2 from a source 72 are applied to a circuit 74, which provides a time delay for these pulses as a linear function of input voltage. The input voltages here are analog signals from the source 75. The location at which a spot is written relative to the end of the delay line will be determined by how long the pulse from source 62 travels from resistor 64 along delay line 60 before the new delayed pulse from time-delay circuit 74 is applied to the entire delay line. During this time, of course, the styli pulses are following in synchronism, as previously explained. Any monostable circuit with a linear electrically controlled time delay, such as emitter-coupled multivibrators, or the phantastron, can be used in this system as a voltage-controlled time-delay circuit.

The significant advantage of the system shown in FIG- URE 2 is that the total number of independent styli is the product of the number of taps times the number of styli connected to each tap, or the number of groups of styli times the number of styli in each group. It should also be noticed that this system requires a triple coincidence. Thus, if desired, independent variation of the video pulse with respect to the sources of positive and negative pulses may be employed to determine which one of the styli will cause writing.

One difficulty with any of the segmented back-bar arrangements is that the region where a pulse is leaving one segment of the back bar and building up on the next backbar segment may cause a stylus in each adjoining group to be subject to the same Writing signal, if due care is not taken, thus causing an erroneous image to appear. This problem can be simply solved by having each array of styli correspond to one and a fraction or two back-bar segmentsfi'ather than one. As such, a pulse simultaneously appearing on two segments causes no difficulty. The total number of styli will then be as low as half the produce of the number of taps on each line, requiring somewhat more taps on each line.

There has accordingly been shown and described hereinabove a novel, useful, and inexpensive system for increasing the writing density of an electrostatic-writing system of the type which employs a tapped delay line with a stylus connected to each tap.

We claim:

1. An electrostatic writing transducer comprising a first delay line having a plurality of taps along the length thereof, a plurality of bus bars a diiferent one of which is connected to each of said taps, a plurality of groups of Writing styli, a different one of the writing styli in each group being connected to a different one of said bus bars,

said groups of styli extending from said bus bars to a common plane, a conductive bar for each group of writing styli, each said conductive bar being positioned opposite a group of writing styli at said common plane, a second delay line having a plurality of taps therealong, the number of said second delay-line taps corresponding to the number of conductive bars, means for connecting each conductive bar to a different one of said taps, and means for applying signals to said first and second delay lines to enable electrostatic discharges to occur between said styli and said conductive bars in a preordered sequence including a first source of pulses having one polarity, means for applying pulses from said first source to one end of said first delay line, a second source of pulses having a polarity opposite to said one polarity, means for applying pulses from said second source to one end of said second delay line, a source of intelligence signals, and means for applying said intelligence signals to both ends of said second delay line to cause an electrostatic discharge between a stylus and conductive bar only in the presence of a first and second pulse and an intelligence signal.

2. In an electrostatic writing system of the type employing a multitapped delay line with styli connected to said taps, said styli extending to a writing location at which they are opposed by conductive bar means, the improvement comprising a first source of pulse signals, means for applying pulse signals from said first source to one end of said tapped delay line at one frequency, a second source of pulse signals, a source of intelligence signals, and means for applying signals from said second source of pulse signals and from said source of intelligence signals to said conductive bar means to effectuate a discharge between a stylus and said conductive bar means only in the presence of all three signals.

3. A system as recited in claim 2 wherein said means for applying signals from said second source of pulse signals and from said source of intelligence signals to said conductive bar means includes a modulator circuit having its output connected tosaid conductive bar means, and means for applying signals from said second source of pulse signals and from said source of intelligence signals to said modulator circuit.

4. A system as recited in claim 2 wherein said means for applying signals from said second source of pulse signals and from said source of intelligence signals to said conductive bar means includes a second tapped delay line, means connecting the taps of said second tapped delay line to said conductive bar means, means for applying pulse signals from said second source of pulse signals to one end of said second tapped delay line, and means for applying signals from said source of intelligence signals to both ends of said second tapped delay line.

References Cited by the Examiner UNITED STATES PATENTS 2,919,171 12/59 Epstein et al. 34674 2,955,894 10/60 Epstein 34674 3,012,839 12/61 Epstein et al. 346-74 3,034,124 5/62 Anderson 346-74 3,068,479 12/62 Benn et a1. 34674 IRVING L. SRAGOW, Primary Examiner. 

1. AN ELECTROSTATIC WRITING TRANSDUCER COMPRISING A FIRST DELAY LINE HAVING A PLURALITY OF TAPS ALONG THE LENGTH THEREOF, A PLURALITY OF BUS BARS A DIFFERENT ONE OF WHICH IS CONNECTED TO EACH OF SAID TAPS, A PLURALITY OF GROUPS OF WRITING STYLI, A DIFFERENT ONE OF THE WRITING STYLI IN EACH GROUP BEING CONNECTED TO A DIFFERENT ONE OF SAID BUS BARS, SAID GROUPS OF STYLI EXTENDING FROM SAID BUS BARS TO A COMMON PLANE, A CONDUCTIVE BAR FOR EACH GROUP OF WRITING STYLI, EACH SAID CONDUCTIVE BAR BEING POSITIONED OPPOSITE A GROUP OF WRITING STYLI AT SAID COMMON PLANE, A SECOND DELAY LINE HAVING A PLURALITY OF TAPS THEREALONG, THE NUMBER OF SAID SECOND DELAY-LINE TAPS CORRESPONDING TO THE NUMBER OF CONDUCTIVE BARS, MEANS FOR CONNECTING EACH CONDUCTIVE BAR TO A DIFFERENT ONE OF SAID TAPS, AND MEANS FOR APPLYING SIGNALS TO SAID FIRST AND SECOND DELAY LINES TO ENABLE ELECTROSTATIC DISCHARGES TO OCCUR BETWEEN SAID STYLI AND EACH CONDUCTIVE BARS IN A PREORDERED SEQUENCE INCLUDING A FIRST SOURCE OF PULSES HAVING ONE POLARITY, MEANS FOR APPLYING PULSES FROM SAID FIRST SOURCE TO ONE END OF SAID FIRST DELAY LINE, A SECOND SOURCE OF PULSES HAVING A POLARITY OPPOSITE TO SAID ONE POLARITY, MEANS FOR APPLYING PULSES FROM SAID SECOND SOURCE TO ONE END OF SAID SECOND DELAY LINE, A SOURCE OF INTELLIGENCE SIGNALS, AND MEANS FOR APPLYING SAID INTELLIGENCE SIGNALS TO BOTH ENDS OF SAID SECOND DELAY LINE TO CAUSE AN ELECTROSTATIC DISCHARGE BETWEEN A STYLUS AND CONDUCTIVE BAR ONLY IN THE PRESENCE OF A FIRST AND SECOND PULSE AND AN INTELLIGENCE SIGNAL. 